metainfo: Add <translation> tag
metainfo: Add <translation> tag

This allows the software repository, such as Debian, Fedora or Flathub,
to extract data about the app's translation coverage; in turn, the
software centre (such as GNOME Software) can indicate to the user
whether the software is available in their language.

See
https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-translation
for more details.

gobby/gobby,gobby/gobby,gobby/gobby